This application seeks support for years 31-35 of a T32 grant for postdoctoral research training for MD, PhD and MD/PhD scientists. The training centers in the Department of Pathology and Immunology at Washington University in St. Louis. We have 28 faculty, distributed among seven departments, with highest representation in Pathology and Immunology. The faculty is made up of a highly interactive group of immunologists and cell/molecular biologists who have collaborated for several years. The research of much of the faculty is on various aspects of immunology, host resistance, and cancer but also includes heavy emphasis on the molecular basis of cell activation (for example our projects focus on host responses to tumors and viruses, lymphocyte differentiation and activation, cell biology and biochemistry of antigen processing, and the analysis of cell interaction molecules). There are two types of trainees-(a) those with either MD or MD/PhD degrees who seek an in-depth experience in research following their clinical training in Pathology or (b) those with PhD and/or MD degrees, not associated with Pathology clinical training, who have an interest in the research done by our faculty members. We have a yearly applicant pool of about 200 qualified individuals who compete for a total of 103 postdoctoral slots among the 28 laboratories. Of these, ten/year were and are supported by this training grant. We request renewal of our ten training positions. A Steering Committee of six senior faculty members oversees the training and is responsible for the selection of trainees. Training includes a 2-3 year period of full-time laboratory research, where the trainee is exposed to the latest approaches in immunology and cell and molecular biology (e.g., transgenic and knockout mice, tumor immunology, DNA technology). Part of the training includes laboratory meetings and reports, participation in weekly seminars, training in research ethics and opportunities for courses in Cancer Biology and Immunology. Of the 49 trainees that have been supported by this Program in the last 10 years, 98% continue in research. The 28 trainees in the Program over the last five years published 40 papers and review articles: 25% in high impact journals and 37.5% involved two or more training faculty. Seventy one percent of our trainees supported during the last 10-years have completed the Program (29% are still in training). Of the former, 74% hold faculty positions, mostly in Pathology. This successful Training Program is thus producing the next generation of basic and clinician scientists who will elucidate many of the heretofore unknown mechanisms that lead to cancer development and/or discover novel therapeutic strategies that can be used to treat neoplastic disease.